Process for the temperature-dependant actuation of an additional pressure medium source in slip-controlled motor vehicle braking systems, and breaking system for the implementation of this process

ABSTRACT

Process for temperature-dependent actuation of a supplemental pressure medium source in slippage-controlled motor vehicle braking systems. The invention pertains to a process for operating a slippage-controlled motor vehicle braking system with regulation of driving dynamics. In such systems it has thus far been proposed to turn on supplemental pressure medium sources to support the supply pump when regulation starts, in order to shorten the regulation time. Practical studies have shown that such supplemental sources are, first of all, not needed for each regulation process and, second, cause disruptive noise. The invention thus proposes to turn on the supplemental pressure medium source only in the presence of special situations, such as if the pressure medium is very viscous due to low temperatures. Advantageous refinements are concerned with determination of the temperature.

TECHNICAL FIELD

The invention pertains to a process for operating a slippage-controlledmotor vehicle braking system for controlling driving dynamics, in whichthe desired pressure at the motor vehicle brake to be controlled is set.

BACKGROUND OF THE INVENTION

In order to shorten the control time, particularly in case of highviscosity of the pressure medium, it was proposed in P 44 25 578.0 (P7697) to turn on a supplemental pressure medium source at the beginningof the braking process which quickly makes available the requiredpressure of the pressure medium. As described in detail in the aforesaidP 44 25 578.0, such a measure offers the great advantage that theresponse of the regulation at the brakes can be considerablyaccelerated, even in the case of high viscosity of the pressure mediumand thus considerable pressure losses due to the sluggish flow of thepressure medium inside the pressure lines.

It has turned out to be a certain disadvantage, however, that turning onsuch a supplemental pressure medium source can cause noise that maydistract the driver precisely at the moment in time in which he is in acritical driving situation in need of regulation.

The object of the invention is to connect the supplemental pressuremedium source to the control loop only if this is actually necessary toaccelerate the regulation process.

This object is achieved, according to the invention, by turning on thesupplemental pressure medium source as a function of a sufficientlylarge deviation from the desired value of the regulation parameter fordriving dynamics, and a second factor which constitutes a measurement ofwhether turning on the pressure medium source is necessary forincreasing the regulation rate under the environmental conditions. Theinvention brings the additional advantage that the supplemental pressuremedium source is not operated unnecessarily and thus is under lessmechanical stress, which contributes to increasing its reliability andservice life.

In practice, it has proven particularly reasonable to make theconnection of the supplemental pressure medium source dependent on theviscosity of the pressure medium. One parameter affecting the viscosityis the temperature of the pressure medium itself, so that it isadvisable as an advantageous refinement of the invention to makeconnection dependent on the pressure medium temperature.

In order to save on additional sensors for measuring temperatures, theexisting engine intake air temperature sensor can be used for estimatingthe temperature of the pressure medium.

Another possibility of estimating the temperature of the pressure mediumconsists of measuring wheel and vehicle response times according to thelatter principle, the regulation behavior is evaluated for estimatingthe temperature.

In a preferred embodiment, the supplemental pressure medium source isactivated only if the temperature of the pressure medium falls below apre-determined temperature.

A particularly advantageous refinement of the invention is presented ifthe connection of the supplemental pressure medium source is madedependent on an additional parameter which corresponds to the gradientof the deviation of the actual value from the desired value of thecontrol parameter. In other words, if the actual value of the drivingdynamics parameter, such as the yaw angle velocity, differs onlyslightly from the desired set value, then it is not necessary for theregulation to take effect abruptly due to turning on the supplementalpressure medium source. Instead, it is then sufficient for theregulation to be operated only with the aid of the supply pump as apressure medium source. The advantage is that in this way the regulationnot only operates rather quietly, but also corrects the driving behaviorof the vehicle more gently. This further contributes to the drivingcomfort of the operator. It is particularly advisable here as arefinement of the invention to make turning on the supplemental sourcedependent on the gradient of the difference of (one of the) followingparameters: the steering angle, the yaw angle or the yaw angle velocityof the vehicle. The invention can also be applied advantageously if,instead of that, the gradient of the difference of the transverseaccelerations of the vehicle or of the velocities of the vehicle servesas the criterion for turning on the supplemental pressure medium source.

An additional improvement of the invention can consist in making theadditional parameters on which the turning on of the supplemental sourcedepends not dependent or not solely dependent on the gradient of thedriving parameter to be regulated, but (additionally) on thetemperature. This may be the environmental temperature of the vehicle,but also the temperature of the pressure medium. In this way it ispossible, for instance, to turn on the supplemental source foraccelerating the regulation only if either the gradient of the deviationof the parameter to be regulated has achieved a certain value or thetemperature lies beneath a certain value. Of course, a mixed parametercan be formed here which depends on both values, so that the lower theenvironmental temperature, the smaller the gradients for turning on thesupplemental source. The application of the process according to theinvention is practical in particular for a braking system wherein thegradient of the deviation of the actual value of the regulated parameterfrom that of the set value.

The invention has proven itself very well for a supplemental pressuremedium source when the deviation from the yaw angle, transverseacceleration, steering angle, or velocity is monitored because theswitching noises of the source are avoided, and the driving comfortduring the case when the vehicle must be regulated is increased.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic of the control system of the present invention.The drawing shows a control loop 1 which is equipped with a supply pump3 to provide the necessary regulated pressure. As soon as the deviationA of the measured actual value of the regulation parameter from the setvalue reaches a sufficient magnitude, the supply pump starts up andprovides an individual braking pressure to the individual wheel brakes 4which is appropriate to return the actual value of the regulationparameter to the specified set value.

In FIG. 1, a switch 5 is also illustrated which switches a supplementalsource 6 into the control loop 1 as a function of the detectedtemperature of the pressure medium, so that the pressure necessary forthe regulation is made available more quickly and thus the regulationspeed is increased.

Details of the mode of functioning of the control loop and the supplypump in conjunction with the wheel brakes and the supplemental sourceare explained in principle in the above-specified P 44 25 578.0 andshould thus not be repeated at this point.

We claim:
 1. Process for operating a slippage-controlled motor vehiclebraking system with regulation of the driving dynamics having, inaddition to a supply pump serving braking pressure regulation in caseregulation is required, a supplemental pressure medium source which,temporarily before or in parallel with the supply pump, emits pressuremedium under pressure serving for regulating the braking pressure invehicle brakes, comprising:means for activating the supplementalpressure medium source as a function of a magnitude of a deviation (A)of an actual value of a regulation parameter from set values, and meansfor activating the supplemental pressure medium source as a function ofthe magnitude of an additional parameter (T); and wherein the parameterdependent on the regulation parameter depends on the viscosity of thepressure medium in the braking system.
 2. Process according to claim 1wherein the additional parameter corresponds to the temperature of thepressure medium in the braking system.
 3. Process according to claim 2,wherein the air intake temperature of the motor vehicle is measured inorder to determine the additional parameter.
 4. Process according toclaim 2, wherein the pressure detected from the wheel and vehiclereactions before the regulation intervention is compared to the wheelpressure estimated from the regulation model for the pressure on thewheel brake, and the temperature is estimated based on the ascertaineddeviation of the temperature.
 5. Process according to claim 1, whereinthe supplemental pressure medium source can be turned on only if thetemperature of the pressure medium falls below a specified value. 6.Process according to claim 1, wherein the supplemental pressure mediumsource is turned on only if the temperature of the pressure medium has avalue below 0° C.
 7. Process according to claim 1, wherein theadditional parameter depends on the gradient of the deviation of theactual value of the regulated parameter from the set value.
 8. Processaccording to claim 7, wherein the additional parameter corresponds todeviation of the yaw angle velocity or the deviation of the transverseacceration or the deviation of the steering angle or the deviation ofthe velocity.
 9. Process according to claim 1, wherein the additionalparameter depends both on the gradient of the deviation of the actualvalue of the regulated parameter and on environmental temperature,specifically, the temperature of the pressure medium.
 10. Braking systemfor performing the process according claim 1, wherein the supplementalpressure medium source is a high-pressure reservoir and/or a brakingforce booster to be turned on and off preferably by the braking pressureregulation.
 11. Braking system according to claim 10, wherein thebraking force booster is a pneumatic braking force booster whose outputis coupled to the control loop by way of a master cylinder.